Maternal aggression (protection of offspring) provides a nexus for understanding two important mental health issues: emotional changes that occur during the postpartum period and fierce reactive aggression. Maternal aggression (also called maternal defense) is a powerful form of reactive aggression that is produced in the defense of offspring and is highly conserved in mammals ranging from humans to mice. Our long-term goal is to understand the functional neuronal circuitry of maternal aggression. The objective of this application is to determine how beta adrenergic and GABA A receptor signaling in lateral septum (LS) act to regulate maternal aggression. The central hypothesis of the application is that lowering of beta adrenergic receptor signaling in LS is a key step for elevating maternal aggression, while lowering GABA A receptor signaling in LS is a key step in reducing aggressive output. LS contains a large number of GABA-positive neurons, many of which project outside of LS, and we propose that these GABA-positive projection neurons contain and are regulated by beta adrenergic and GABA A receptors in LS. The rationale for the proposed research is that once the mechanisms by which beta adrenergic and GABA A receptors regulate maternal aggression in LS are known, we will gain important insights into neuronal changes during lactation that shed light on postpartum mood disorders. We will also gain information on the basis of fierce reactive aggressive outburst in humans that is expected to provide insights into new interventions. Consequently, the proposed research is relevant to NIH's mission to reduce the burden of mental illness and behavioral disorders. Guided by strong preliminary data, the hypothesis will be tested by pursuing two specific aims: 1) Identify the key receptors that act in LS to regulate maternal aggression; and 2) Identify the neuronal population in LS that is regulated by beta adrenergic and GABA A receptors. Under the first aim, site-specific injection approaches will be used to modulate beta adrenergic and GABA A receptor activity and test effects on maternal aggression. Established Western blotting and real-time PCR techniques will be used to determine the extent to which these receptors show altered expression in association with changes in aggression. Under the second aim, gene expression approaches will be used to identify changes in GABA synthesis that occur in LS in association with changes in aggression. Double/triple labeling approaches along with anterograde and retrograde tracing will be used to determine the extent to which GABA-positive neurons in LS contain GABA A and beta adrenergic receptors and to identify the downstream brain regions that are targets of the GABA-positive projection neurons in LS. The proposed work is innovative because it combines an array of behavioral, pharmacologic, neurobiological, and neurochemical methods to examine an important, but understudied area of maternal aggression. The proposed research is significant, because it will provide critical missing information on how fierce reactive aggression is produced and provide insights into mood changes during the postpartum period.